What is toxicology? - PowerPoint PPT Presentation

What is toxicology?. toxic compounds. physical agents. `. toxicology … ……… • Is the study of the harmful effects of chemicals and physical agents on living organisms • Examines adverse effects ranging from acute to long-term

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The commonly used time unit is one day and thus, the usual dosage unit is mg/kg/day.

Environmental exposure units are expressed as the amount of a xenobiotic in a unit of the media. mg/liter (mg/l) for liquids

mg/gram (mg/g) for solids

mg/cubic meter (mg/m3) for airOther commonly used dose units for substances in media are parts per million (ppm), parts per billion (ppb) and parts per trillion (ppt).

Fractionatinga total dose usually decreases the probability that the total dose will cause toxicity. The reason for this is that the body often can repair the effect of each subtoxic dose if sufficient time passes before receiving the next dose. In such a case, the total dose, harmful if received all at once, is non-toxic when administered over a period of time. For example, 30 mg of strychnine swallowed at one time could be fatal to an adult whereas 3 mg of strychnine swallowed each day for ten days would not be fatal.

The Classical LD50 test is used to determine the lethal dose (LD50) of a substance that will kill 50% of test animals. Typically, this method can use 100 or more animals. The test material is administered in increasing doses, usually 5 or more, to groups of 10 male and 10 female animals. Mortalities are recorded within a given period, and the LD50 is determined with the aid of statistical calculations.

Acute toxicity test in which, if no ill-effects occur at a pre-selected maximum dose, no further testing at greater exposure levels is required.

Five to ten animals of each sex or 10 animals of the susceptible sex are administered a dose specified by regulations. Toxic responses occurring within a given period are recorded. Based on the results, a regulatory action or additional testing may be required.

When compound related mortality occurs in the limit test, then 5 animals per dose, at least 3 dose levels are used to produce a range of toxic effects and mortality rates; clinical observations and pathological investigations are conducted.

A fixed dose procedure, which uses morbidity instead of mortality as the end point, is also recommended.